The invention relates generally to a method and system of packaging oxygen sensitive materials, and particularly to a method and system for triggering an oxygen scavenging component of a container for containing oxygen sensitive materials.
It is well known that limiting the exposure of oxygen sensitive products to oxygen maintains and enhances the quality and shelf life of the product. For instance, by limiting the oxygen exposure of oxygen sensitive food products in the packaging system, the quality of the food product is maintained and spoilage is reduced. In addition, such packaging also keeps the product in inventory longer, thereby reducing costs incurred from waste and having to restock. At present, commonly used packaging systems include modified atmosphere packaging (MAP) and vacuum packaging in conjunction with oxygen barrier films. In these instances, reduced oxygen environments are employed at the time of packaging, while the oxygen barrier film reduces the amount of oxygen that physically enters the package during storage.
U.S. Pat. No. 5,211,875 to Speer et al. and PCT publication WO 94/12590 disclose methods and compositions for scavenging oxygen. The "oxygen scavenger" materials disclosed by Speer et al. are compositions which consume, deplete or reduce the amount of oxygen from a given environment.
Oxygen scavenging materials are useful in MAP and barrier packaging environments. However, problems are encountered when the oxygen scavenging material is a component of the inner wall of a pre-formed container. The difficulty arises in exposing the internal oxygen scavenging component to a uniform dosage of actinic radiation so that consistent initiation of oxygen scavenging activity across the internal surface is achieved.
The need remains for an effective method of triggering the oxygen scavenging activity of an internal oxygen scavenging component of a pre-formed container.
"Trigger" and the like herein mean that process defined in U.S. Pat. No. 5,211,875, whereby oxygen scavenging is initiated by exposing a composition, film, etc. to actinic radiation having a wavelength of less than about 750 nm at an intensity of at least about 1.6 mW/cm.sup.2 or an electron beam at a dose of at least about 0.2 megarads, wherein after initiation the oxygen scavenging rate is at least about 0.05 cc oxygen per day per gram of oxidizable organic compound for at least two days after oxygen scavenging is initiated. Preferred is a method offering a short "induction period" (the time that elapses, after exposing the oxygen scavenging component to a source of actinic radiation, before initiation of the oxygen scavenging activity begins) so that the oxygen scavenging component can be activated at or immediately prior to use during filling and sealing of the container with an oxygen sensitive material; a method wherein the oxygen scavenging material is substantially consistently triggered across the entire internal surface of the preformed container; a method which is simple and readily incorporated into existing packaging procedures; and a method which is readily incorporated in-line into existing packaging systems.